Medication is often dispensed using a unit dose medical cartridge, such as an ampule, vial or syringe, and a syringe holder, injector or adapter. The cartridge typically has a barrel with a needle at one end and a plunger at the other end. Such cartridges are often referred to as "pre-filled syringes" because they contain a specific dosage or volume of medication when they are initially provided, as compared to conventional syringes which are furnished empty and filled by the user prior to use. Alternatively, the medical cartridge may include a rubber stopper instead of a needle and/or may include a piston rather than a plunger on the other end. The syringe adapter is typically a hollow body adapted to hold the cartridge, including a plunger to engage and move the piston in the cartridge.
Because of the threat of communicable diseases, a number of syringes and adapters have been developed to prevent accidental needle sticks or inadvertent reuse of needle devices. Many of these devices, however, are not easy to use or are complicated to manufacture. For example, U.S. Pat. No. 5,569,211 discloses a syringe that allows the needle of the syringe to be withdrawn into the barrel of the syringe after medication is dispensed from it. This device, however, is a specially designed substitute for a conventional syringe, and cannot be used to hold commercially available pre-filled syringes or ampules.
U.S. Pat. No. 5,522,812 discloses a complicated syringe shield device for holding a conventional cartridge not having its own needle. The device has a number of complicated parts, including a cylindrical body, a double needle assembly, a cylindrical shield, a special collar piece allowing the shield to be drawn over the needle and locked, and a plunger assembly, resulting in a device that is potentially difficult and expensive to manufacture. The device also requires two hands to operate, one to hold the body, and one to rotate the shield into the locked position, which may be inconvenient to the medical professional using the device.
Another consideration with unit dose cartridges and prefilled syringes is that they are often made from glass, particularly for holding certain vaccines or biotech drugs where concern about micro-organisms or other contaminants is most critical. Glass pre-filled syringes may be particularly fragile and often may break during transportation or use. Some existing adapters may not adequately protect the syringe contained therein from such risks. Others, provide greater protection for the cartridge, but may obstruct the medical professional's view of the syringe when the device is being used, hampering monitoring of the medication being delivered.
Therefore, there is a need for an improved safety syringe which is inexpensive and simple to manufacture.
In addition, there is a need for a syringe guarding mechanism which provides improved protection for the cartridge or pre-filled syringe therein, but allows effective observation of the syringe and the medication being dispensed.